1. Field of the Invention
This invention relates to apparatus for automatically activating an alarm when the heat of a kiln reaches a pedetermined level.
2. Description of the Prior Art
Kilns are used by ceramic artists and hobbyists for the firing of ceramic products. Various automatic control systems for turning off kilns are known. Typically, an element of such a control system is a pyrometric cone composed of a fusible material which deforms upon exposure to a predetermined amount of heating. The deforming of the cone permits movement of a lever activating a shut off mechanism. An automatic shut off system when a predetermined level of heating is reached in a kiln as disclosed in U.S. Pat. No. 2,675,600 issued to W. P. Dawson on Apr. 20, 1954. The melting or deforming of the cone permits a lever to move and to release a weighted arm which swings downward by gravity. The weighted arm is mounted to the outside of the kiln. The moving lever in the Dawson patent is pivoted at an intermediate point between the one end of the lever resting on the cone and the other end of the lever restraining the swinging weighted arm. Two brackets are inserted into slots in an interior end of a ceramic tube to support the cone. A relatively small torque is available to cause movement of the lever to release the weighted arm because the lever is almost at balance about the pivot point. A somewhat longer extension of the lever from the pivot point to the tyrometric cone than from the pivot to the weight releasing end causes the weight releasing end to move upward.
U.S. Pat. No. 2,555,864 issued to C. H. Strange on June 5, 1951 discloses a similar system which utilizes the collapse or melting of a pyrometric cone to move a rod and to actuate an electric switch which then energizes an electric device which can shut off the heat supply to the kiln and energize a warning signal. As before, a special support is required for the pyrometric cone and relatively little torque can be produced by the pivoting rod.